Apparatus including a magnet clamp for indicating an electrically grounded condition



Aug. 30, 1966 c, z WALSH 3,270,332

APPARATUS INCLUDING A MAGNET CLAMP FOR INDICATING AN ELECTRICALLYGROUNDED CONDITION Original Filed Feb. 13, 1961 2 Sheets-Sheet 1 C. 2.WALSH Aug. 30, 1966 3,270,332

APPARATUS INCLUDING A MAGNET CLAMP FOR INDICATING AN ELECTRICALLYGROUNDED CONDITION Original Filed Feb. 13, 1961 2 Sheets-Sheet 2 UnitedStates Patent 3,270,332 APPARATUS INCLUDING A MAGNET CLAMP FORINDICATING AN ELECTRICALLY GROUNDED CONDITION Carl Z. Walsh, Warwick,.R.I., assignor to Texaco Inc., ;New York, N.Y., a corporation ofDelaware Continuation of applicationSer. No 88,937, Feb. 13, 1961. Thisapplication Mar. 10, 1964, Ser. No. 351,886

' 8 Claims. (Cl. 340255) This invention relates generally to anapparatus indicating the grounding of an electrostatically charged body,e.g., a tank truck or a marine or aeronautic vessel used to transportvolatile petroleum products, and in one specific aspect, to an attachingmeans for such an apparatus.

This is a continuation application of my copending application forpatent, Ser. No. 88,937, filed February 13, 1961.

Many tests indicate that the majority of tank truck transportersentering a petroleum products loading rack carry a substantialelectrostatic charge, which, if not dissipated before the loadingprocedure begins, may cause a fire or explosion, should there be anelectrostatic discharge du-ring the loading of the products. Thisdischarge may occur between the loading spout and the opening of a tankcompartment, or between the rack structure or an individual contacting atruck transporter to result in the ignition of vapors within the trucktransporter or of those vapors flowing to the ground.

A static charge can be accumulated also by the flow of petroleumproducts into the tank truck transporter compartments during the loadingperiod. If such a charge is not drained off continuously through anelectrical grounding arrangement, it may build up to a point where itwill discharge to ground and result in an explosion and/ or fire.

Accordingly, it is an overall object of the present invention to providean improved means for dissipating the electrical charge which may existon a volatile combustible tank truck transporter at the time it entersthe loading rack or a marine vessel at dockside and/or which may developduring the loading operation.

Another object of the invention is to provide an improved electricalgrounding arrangement which is dependable and indicates that anelectrical circuit through a charged body to ground is not interrupted.

Still another object of the invention is to provide an effectiveelectrical grounding circuit with means for indicating when such acircuit is completed.

Another object of the invention is to provide an electrical groundindicating apparatus which is simple to construct and economical tooperate.

And still another object of the invention is to provide an improvedmeans for interconnecting an electrical ground indicating apparatus withan electrically charged member.

These and other objects, advantages and features of the invention willbecome apparent from a consideration of the specification in the lightof the figures of the accompanying drawings wherein:

FIG. 1 is a simplified showing of the basic circuit of my electricalground indicator;

FIG. 2 is a showing of a modification of the circuit of the groundindicator disclosed in FIG. 1;

FIG. 3a is a perspective view of a magnetic grounding clamp for use withmy electrical ground indicator;

FIG. 3b is a sectional view of the grounding clamp taken along the line3b3b of FIG. 3a; and

FIG. 4 is a diagrammatic disclosure of the installation of theelectrical ground indicator.

The objects of my invention are achieved by the use of relay controlmeans which, in response to the com- "ice pletion of an electricalcircuit to ground by the attachment of a magnet clamp to an electricallycharged member, actuates a circuit to indicate the electrically groundedcondition of the member.

Referring to FIG. 1, there is disclosed the basic circuit of myelectrical ground indicator, including a transformer at 10, with itsprimary winding at 11 furnished with power by connection at theterminals 12 and 13, such power being obtained, for example, from asource of volt, 60 cycle alternating current. The secondary winding 14of the transformer 10 steps down the 120 V. AC. supply to a nominalvoltage of approximately 5 volts, with one terminal of the secondarywinding being grounded at the terminal 15, while the other terminal isconnected in series with a resistor 16, a relay coil 17, and a terminalat 18. A grounding clamp (not shown), adapted to be attached to themember or object to be electrically discharged to ground, is connectedacross the terminals 15 and 18. In response to the fiow of current whenthe ground circuit is completed through the charged member by attachmentof the clamp to the member to be electrically discharged and across theterminal 15 and 18, the relay coil 17 actuates the relay switch 19 inthe indicating circuit, shown generally at 20, which has a lamp 211 inseries therein and is connected across the source of power for thetransformer, at 1-2 and 13'. It is possible to replace the lamp by otherindicating means, as, for example, audible means such as a buzzer or abell, or an electrical set up for controlling the operation of theloading pump, e.g. by another relay means.

There is disclosed in FIG. 2, a refinement of the basic electricalground and indicating circuit of FIG. 1, to include an explosion proofcontainer 22, and with the same enumeration for the same or similarelements disclosed in FIG. 1. These include a hermetically sealedtransformer at 10, indicated by the dotted outline, with the same 120 V.AC. power supply to the primary winding 11 and across which theindicating circuit 20 is shown connected at 12' and 13. The secondarywinding 14 of the transformer 10 is connected at one of its terminals toground, as at 15a, while the other terminal is connected in series to aresistor 16, a rectifier 23, and a contact at 2-4. The series circuit iscontinued therefrom through one of a pair of conductors at 25, whichconductors are joined to conductor rods at a magnet clamp 30. The freeend of the other of the pair of conductors is connected to the ground at15b. The relay coil 17 is connected to the output of the rectifier 23and actuates the relay switch at 19 to complete the indicating circuit20 with the lamp at 21. In conjunction with the conductors 25, there isdisclosed a take up reel 25a on which the excess of the pair ofconductors maybe stored. The combination of the rectifier, relay coiland switch may be positioned in a sealed container, shown in dottedoutline.

Referring to FIGS. 3a and 3b, the magnet clamp 30 consists of a pair ofcontact point assemblies 31 which are unitized by a pair of yokes 32,joined together by threaded means, e.g., a nut and bolt assembly at 32a,and a carrying handle 33 joined to said yokes. Each contact pointassembly consists of a cylindrical permanent magnet 34, with an axialbore 34a, housed in a Bakelite sleeve 35. The axial bore 34a receivesthe conductor rod 36 of T-shape configuration and is preferably bronze,with a Stellite contact point at 36a at the T-end, with this end of therod working in an appropriate shaped slot 34b in the magnet 34. The rod36 is kept in resiliently mounted assembly by the screw nut and washer,at 37a and 37b respectively, and-the loading springs at 38a and 3811.One end of the conductors 25 is fastened to an end of each plunger rod36 of the assemblies 31, and is shown soldered at 39, although the nutand washer at 3711 and 3711 could be used as a terminal connection toreceive the conductors ends, for ease of maintenance.

In use, the magnet clamp is placed on the tank transporter to be loaded,.and normally the indicating circuit will light up showing that there isa good contact and that the transporter is grounded. If there is nolighting (or other indication), slight movement of the clamp will causethe contact points to dig through paint or dirt to obtain a good contactand so lead to an indication of grounding. In case the tank transporteris made of aluminum or other non-ferrous material, the weight of themagnet clamp is enough to make contact through the point 36a, andusually dome cover assemblies are constructed of a ferrous material towhich the magnet clamps will hold. With this type of clamp, positivedisengagement, because of careless loading, is unnecessary.

In operation, the electrical ground circuit is completed by theapplication of the magnet clamp 30 to the member to be grounded, e.g.the magnets 34 are positioned engage a part of a tank truck 26 or restthereon. When the contact point engagement is made, a minute amount ofcurrent (of about .0015 ampere) flows from one contact point of theclamp through the portion of the truck or other charged body to begrounded and out of the other contact point of the clamp through one ofthe pair of conductors to the ground connection at 15b. The small amountof current flow causes the relay to operate, closing the switch at 19,completing a circuit and so energizing the indicating means to show thatan electrical ground has been established. With the low voltage ofapproximately volts and the small amount of current drawn by the relay,it is virtually impossible to obtain a spark when making or breaking thecontact with the truck. As mentioned for FIG. 1, the relay coil may beutilized in a control scheme to interlock the operation of a solenoidvalve to prevent the loading operation from taking place unless thetruck has been grounded electrically.

As disclosed in FIG. 2, there are separate ground contacts at a and1511, respectively for one end of the secondary winding of thetransformer and for one of the pair of conductors in order to assure thecomplete electrical grounding of the charged member, even though it maybe possible to interconnect the ground connection as indicated by thedotted line at 15c.

FIG. 4 is a diagrammatic showing of the installation of 'my improvedelectrical ground indicator at a loading rack. The ground indicator inits explosion proof container is at 22, with the indicating light orother means at 21. the double conductors at 25, with the take up reel at250, and the magnet clamp at for engagement with a tank truck at 26.

Thus there has been shown and described a device for obtaining areliable static ground on a tank truck or other receptacle whichcontains volatile combustible products and is capable of building up anelectrical charge, with an indication that an electrical charge, with anindication that an electrical ground connection has been made beforefilling operations are started and while filling operations proceed.

Other modifications and variations of the invention, as hereinbefore setforth, may be made without departing from the spirit and scope thereof,and therefore only such limitations should be imposed as are indicatedin the appended claims.

I claim:

1. A device for use in electrically grounding a charged body comprising,in combination, a series circuit through said charged body to groundincluding a source of electrical energy, a relay control means, andmagnetic clamping mean With a ground connection for attachment to saidcharged body for completing said series circuit therethrough to ground,and means, connected across said source of electrical energy, forindicating that said series circuit has been grounded electricallyincluding a switch responsive to said relay control means.

2. In the device defined in claim 1, said clamping means comprising apair of contact point assemblies each containing a permanent magnet anda conductor rod housed therein, the conductor rods being interconnectedinto said series circuit through said charged body at spaced apartpoints.

3. An apparatus for use in electrically grounding a charged bodycomprising the combination of a source of electrical energy including atransformer and a series circuit through said charged body to groundjoined to the output of said transformer including a relay control meansand magnetic clamping means with a ground connection for attachment tosaid charged body for completing said series circuit therethrough toground, and means, connected across said source of electrical energy,for indicating that said series circuit has been grounded electricallyincluding a switch responsive to said relay control means.

4. In the apparatus defined in claim 3, said clamping means comprising apair of contact point assemblies each containing a permanent magnet anda conductor rod housed therein, the conductor rods being interconnectedinto said series circuit through said charged body.

5. In the apparatus as defined in claim 3, one end of said output ofsaid transformer being connected to ground and separate from the groundconnection for said clamp ing means.

6. An apparatus comprising, in combination, a transformer and a sourceof power connected thereto, relay control means, and means for actuatingsaid relay control means interconnected through an electrostaticallycharged member to ground in series with the output of said transformerand comprising a rectifier and clamping means connected to ground forattachment to a charged member to be grounded electrically, said relaycontrol means being responsive to said rectifier, and means, joined tothe input to said transformer, for indicating the electrical groundingof said member when said clamping means have been attached, saidclamping means comprising a magnet clamp including a pair of contactpoint assemblies, and means for joining said assemblies together, saidassemblies each comprising a permanent magnet and a conductor rod housedtherein, the rods of said assemblies being in the series circuitcompleted through said charged body to ground with said means foractuating said relay control means.

7. In the device as defined in claim 6, said rectifier being in serieswith said source of power.

8. An apparatus to discharge and prevent the accumulation of an electriccharge on a body and to indicate its electrically grounded conditioncomprising, in combination, a'source of power including a transformer,means for providing alternating current energy thereto, means forelectrically grounding a body comprising a series circuit of animpedance, a rectifier and clamping means interconnecting one terminalof the secondary winding of said transformer through said body with aground, the other terminal of said secondary winding being joined to aground separate from that of said series circuit, and a relay controlmeans connected across the rectifier output, and means for indicatingthe electrically grounded condition of said series circuit connectedacross said suorce of alternating current energy and being responsive tosaid relay control means upon completion of the series circuit toground, said clamping means comprising a pair of contact pointassemblies each containing a permanent magnet and a conductor rod housedtherein, the conductor rods contacting said body at spaced apart pointsto complete said series circuit therethrough to ground.

No references cited.

NEIL C. READ, Primary Examiner. D. K MYER, Assistant Examiner.

1. A DEVICE FOR USE IN ELECTRICALLY GROUNDING A CHARGED BODY COMPRISING,IN COMBINATION, A SERIES CIRCUIT THROUGH SAID CHARGED BODY TO GROUNDINCLUDING A SOURCE OF ELECTRICAL ENERGY, A RELAY CONTROL MEANS, ANDMAGNETIC CLAMPING MEANS WITH A GROUND CONNECTION FOR ATTACHMENT TO SAIDCHARGED BODY FOR COMPLETING SAID SERIES CIRCUIT THERE-